Disclosed are intermediate transfer members, and more specifically, intermediate transfer members useful in transferring a developed image in an electrostatographic, for example xerographic, including digital, image on image, and the like, machines or apparatuses. In embodiments, there are selected intermediate transfer members comprising a layer or substrate comprising a thermosetting polyimide, and more specifically, an intermediate transfer belt comprised of a conductive component like carbon black, a polyaniline, a carbon nanotube, and the like, or mixtures thereof dispersed in a thermosetting polyimide, which polyimide is cured at low temperatures, such as less than about 290° C., and more specifically, from about 180 to about 260° C., from about 180 to about 215° C., from about 195 to about 225° C., from about 200 to about 250° C., from about 200 to about 210° C., from about 200 to about 205° C. over a short period of time, such as for example, from about 10 to about 120 minutes, and from about 20 to about 60 minutes. The polyimide is available as VTEC™ PI 1388 from Richard Blaine International, Incorporated, Reading, Pa. Conventional thermosetting polyimides, such as KAPTON® polyimides available from E.I. DuPont, are usually cured at high temperatures, such as over 300° C., and more specifically, from about 305 to about 350° C. over a period of time, such as from about 30 to about 240 minutes, from about 25 to about 45 minutes, from about 20 to about 40 minutes, from about 20 to about 100 minutes, from about 15 to about 25 minutes, and from about 60 to about 120 minutes.
A number of advantages are associated with the intermediate transfer member of the present disclosure such as excellent dimensional stability, lower surface friction, and less humidity sensitivity; low temperature and fast curing when compared with the known KAPTON® polyimide member; and more specifically, the polyimide containing intermediate transfer belt possesses in embodiments a surface resistivity of from about 109 to about 1013 ohm/sq (as measured by a High Resistivity Meter under 1,000 volts), a tensile strength of from about 150 to about 400 MPa (as measured by an Instron Tensile Tester, ASTM D-882-91, Method A), and the intermediate transfer members of the present disclosure are weldable while a number of the prior art polyimide containing transfer members are difficult or usually cannot be properly welded. Also, it is believed that a number of the known polyimide transfer belts are free of curing, or not readily curable especially at temperatures below about 300° C.; and should the prior art thermosetting polyimide ITB be even partially cured at less than 300° C., the tensile strength is usually too weak to permit such known polyimides to be used as a functional ITB.
While not being desired to be limited by theory, it is believed that the disclosed polyimide is prepared by the reaction of an aromatic diamine with an aromatic dicarboxylic acid, where either amine or carboxylic acid or both contains a C═C substituting group. Thus, two reactions occur during the less than about 300° C. cure (1) nominal but incomplete imidization; and (2) free radical polymerization of the substituting C═C groups, which permits a high ITB tensile strength. In contrast, for the known polyimides, there exists only a single imidization during cure, and no other crosslinking such as free radical polymerization thus a number of the known polyimide ITB require curing above 300° C. in order to obtain a high tensile strength.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member, and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and colorant, which are commonly referred to as toner. Generally, the electrostatic latent image is developed by bringing a developer mixture into contact therewith. The developer mixture can comprise a dry developer mixture, which usually comprises carrier granules having toner particles adhering triboelectrically thereto, or a liquid developer material, which may include a liquid carrier having toner particles, dispersed therein. The developer material is advanced into contact with the electrostatic latent image, and the toner particles are deposited thereon in image configuration. Subsequently, the developed image is transferred to a copy sheet. It is advantageous to transfer the developed image to a coated intermediate transfer web, belt or component, and subsequently transfer with very high transfer efficiency the developed image from the intermediate transfer member to a permanent substrate. The toner image is subsequently usually fixed or fused upon a support, which may be the photosensitive member itself, or other support sheet such as plain paper.
In electrostatographic printing machines wherein the toner image is electrostatically transferred by a potential difference between the imaging member and the intermediate transfer member, the transfer of the toner particles to the intermediate transfer member and the retention thereof should be substantially complete so that the image ultimately transferred to the image receiving substrate will have a high resolution. Substantially 100 percent toner transfer occurs when most or all of the toner particles comprising the image are transferred, and little residual toner remains on the surface from which the image was transferred.
Intermediate transfer members allow for positive attributes, such as enabling high throughput at modest process speeds, improving registration of the final color toner image in color systems using synchronous development of one or more component colors using one or more transfer stations, and increasing the range of final substrates that can be used. However, a disadvantage of using an intermediate transfer member is that a plurality of transfer steps is required allowing for the possibility of charge exchange occurring between toner particles and the transfer member which ultimately can lead to less than complete toner transfer. The result is low-resolution images on the image receiving substrate and image deterioration. When the image is in color, the image can additionally suffer from color shifting and color deterioration. In addition, the incorporation of charging agents in liquid developers, although providing acceptable quality images and acceptable resolution due to improved charging of the toner, can exacerbate the problem of charge exchange between the toner and the intermediate transfer member.
In embodiments, the resistivity of the intermediate transfer member is within a range to allow for sufficient transfer. It is also desired that the intermediate transfer member have a controlled resistivity, wherein the resistivity is virtually unaffected by changes in humidity, temperature, bias field, and operating time. In addition, a controlled resistivity is of value so that a bias field can be established for electrostatic transfer. Also, it is of value that the intermediate transfer member not be too conductive as air breakdown can possibly occur.
Attempts at controlling the resistivity of intermediate transfer members have been accomplished by, for example, adding conductive fillers such as ionic additives and/or carbon black to the outer layer. For example, U.S. Pat. No. 6,397,034 discloses the use of fluorinate carbon filler in a polyimide intermediate transfer member layer. However, there are problems associated with the use of such additives. In particular, undissolved particles frequently bloom or migrate to the surface of the polymer. and cause an imperfection in the polymer. This leads to nonuniform resistivity, which in turn causes poor antistatic properties and poor mechanical strength. The ionic additives on the surface may interfere with toner release. Furthermore, bubbles may appear in the conductive polymer, some of which can only be seen with the aid of a microscope, others of which are large enough to be observed with the naked eye. These bubbles provide the same kind of difficulty as the undissolved particles in the polymer, namely poor or nonuniform electrical properties and poor mechanical properties.
In addition, the ionic additives themselves are sensitive to changes in temperature, humidity, and operating time. These sensitivities often limit the resistivity range. For example, the resistivity usually decreases by up to two orders of magnitude or more as the humidity increases from about 20 percent to 80 percent relative humidity. This effect limits the operational or process latitude.
Moreover, ion transfer can also occur in these systems. The transfer of ions leads to charge exchanges and insufficient transfers, which in turn causes low image resolution and image deterioration, thereby adversely affecting the copy quality. In color systems, additional adverse results include color shifting and color deterioration. Ion transfer also increases the resistivity of the polymer member after repetitive use. This can limit the process and operational latitude, and eventually the ion-filled polymer member will be unusable.
The use of polyaniline filler contained in a polyimide has been disclosed in U.S. Pat. No. 6,602,156. More specifically, this patent discloses a polyaniline filled polyimide puzzle cut seamed belt. The manufacture of the puzzle cut seamed belt is usually labor intensive and costly, and the puzzle cut seam, in embodiments, is sometimes weak. The manufacturing process for a puzzle cut seamed belt requires an extended high temperature and a high humidity conditioning step. For the conditioning step, each individual belt is rough cut, rolled up, and placed in a conditioning chamber that is environmentally controlled at 45° C. and 85 percent relative humidity, for approximately 20 hours. Another 3 hours are required to bring the belt back down to ambient conditioning to prevent condensation and watermarks before it can be removed from the conditioning chamber. This conditioning operation is selected to result in a belt with an appropriate resistivity range for use in a color printer. The conditioning step also involves that the sheets of the belt material be cut roughly to size prior to conditioning. This renders it difficult to automate the manufacturing process for puzzle cut seamed belts. Without the 24 hour high temperature and high humidity conditioning step, the belt's electrical properties and hence image quality will not be stable for several months.
Small circumference intermediate transfer belts can be obtained by extrusion or spin casting. However, extrusion and spin casting are not cost effective for belts requiring larger circumferences. Larger circumference belts are typically selected for use in color xerographic tandem engine architecture machines.
It is desired to provide a weldable intermediate transfer belt, which has improved transfer ability and permits improved copy quality. It is also desired to provide a weldable intermediate transfer belt that may not, but could, have puzzle cut seams, but instead, has a weldable seam, thereby providing a belt that can be manufactured without labor intensive steps as manually piecing together the puzzle cut seam with fingers, and without the lengthy high temperature and high humidity conditioning steps. It is also desired to provide a higher circumference weldable belt for color machines.